This invention relates to the field of foam materials suitable for sound absorption in automotive and appliance applications.
Materials which are currently used for sound absorption applications in automobiles and appliances have one or more deficiencies. For example, open-cell polyurethane foams and melamine foams are thermoset materials, that is, cross-linked polymers, which are not easily recyclable. In addition, polyurethane and melamine foams lack hydrolytic stability for long term use in contact with water or in a humid environment.
Shoddies are relatively inexpensive fibrous pads, typically made from recycled scrap material by shredding and needling thermoplastic and/or thermoset materials. Although shoddies typically have good sound absorbing properties, they are relatively dense, and add significantly to the weight of a car or an appliance. Further, fibrous materials lack structural integrity and are often difficult to handle.
Open-cell polyolefin foams which are currently available commercially are not well suited for sound absorption. For example, a commercially available open-cell polyolefin foam made from cross-linked polyethylene, which is produced by a compression molding process, has been found unsuitable for sound absorption according to an industry source. It is believed that the pores in this foam are too small to permit an adequate flow of air, which in turn results in poor sound absorption properties.
Therefore, it would be desirable to have an open-cell, low density, recyclable thermoplastic foam exhibiting excellent sound absorption properties for use in automotive and appliance applications. In particular, it would be desirable to provide a polyolefin foam which is substantially non-cross-linked or lightly cross-linked, and which has sufficient open-cells and a sufficient cell size to exhibit high porousity and hence excellent sound absorption properties.
This invention provides an expanded open-cell foam polymer composition comprising at least one linear or modified linear polyolefin, at least 50% of the cells being open, and the cells having an average size of at least 1 millimeter. It is desirable that the composition have a sound absorption coefficient as determined by ASTM D 1050 at 1,000 Hz which is greater than 0.15. In preferred foams the composition has an airflow resistivity of less than about 800,000 Rayls/m.
In another embodiment, this invention provides a sound insulation panel comprising two skin layers and a foam sheet disposed between the two skin layers, the foam sheet comprising an expanded open-cell polymer composition having a sound absorption coefficient as determined by ASTM D 1050 at 1,000 Hz which is greater than 0.15 comprising at least one linear or modified linear polyolefin, at least 50% of the cells being open, and the cells having an average size of at least 1 millimeter. Preferably, the composition has an airflow resistivity of less than about 800,000 Rayls/m.
In another embodiment, this invention provides a foam sheet comprising an open-cell polymer composition having a sound absorption coefficient as determined by ASTM D 1050 at 1,000 Hz which is greater than 0.15 comprising at least one linear or modified linear polyolefin, at least 50% of the cells being open, and the cells having an average size of at least 1 millimeter. Preferably, the composition has an airflow resistivity of less than about 800,000 Rayls/m.
The polymeric foam materials of this invention exhibit excellent sound-absorbing characteristics, excellent hydrolytic stability for long term use in contact with water and a humid environment, and have relatively low density, good structural integrity, and are easy to handle.